Observations of stratospheric and mesospheric O3 with a millimeter-wave radiometer at Rikubetsu, Japan

We have been measuring brightness temperature spectra of the atmospheric ozone (O 3 ) emission at 110.83 GHz with a millimeter-wave radiometer (MWR) located at Rikubetsu, Japan, since November 1999. Tropospheric opacities, which were also measured with the MWR and were used to take into account attenuation of the O 3 signal from the stratosphere and mesosphere, were corrected using the tropospheric opacity calculated from radiosonde data. Temporal variations of the measured spectral intensity of O 3 , likely due to degradations of the superconductor–insulator–superconductor receiver and of the vessel for cold calibration load, were also corrected using scaling factors derived from ozonesonde data up to an average height of 35 km and Microwave Limb Sounder (MLS) monthly mean climatology above the sonde height. The vertical profiles of the O 3 mixing ratio in the altitude range from 24 to 56 km were retrieved from the spectra with the optimal estimation approach. The retrieval errors from uncertainties in the scaling factor, the corrected tropospheric opacity, and atmospheric temperature, as well as those from spectral noise, were evaluated, and we found that the main retrieval errors resulted from uncertainties in the scaling factor and tropospheric opacity. The retrieved O 3 profiles were compared with those from the Solar Backscatter Ultraviolet (SBUV/2), the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER), and the MLS instruments onboard satellites. The retrieved O 3 mixing ratios at individual levels agreed with the MLS version 3.3 or 3.4 data with an average difference better than ±5 % and a standard deviation of 4–9 %. Additionally, the retrieved O 3 profiles were in reasonable agreement with the SABER version 2.0 O 3 profiles and the SBUV/2 version 8.6 O 3 profiles, in line with the validation results of their satellite data in the earlier literature.